Magnetic tenter lever actuating device

ABSTRACT

A magnetic tenter lever actuating device includes a coupling rail, preferably designed in the form of a pole shoe rail (21), by means of which the end of a tenter lever (3) can be pivoted deliberately from its open into its closed position and vice versa by means of a coupling region (29) formed at the end. An improved magnetic tenter lever actuating device is primarily characterized by the following features: 
     the magnetic actuating device for the tenter lever further includes a safety device for actuating the tenter lever, 
     the safety device comprises a mechanically acting redundant system for the forcible opening and/or closing of the tenter lever in the event of the failure or ineffectiveness of the magnetic actuating device, 
     the safety device is arranged and designed such that, when an opening and/or closing movement is to be carried out by means of the safety device, the tenter lever can be pivoted mechanically, at least in its first opening pivoting range, out of its closed position or, at least in its final pivoting range, into its closed position.

The invention relates to a magnetic tenter lever actuating device.

Tenter lever actuating devices, that is to say so-called tenteropeners/closers, are used in transport devices for moving material webs,in particular in stretching systems for plastic film webs.

In the production of plastic film, transverse stretching systems,longitudinal stretching systems and also simultaneous stretching systemsare known, the material web being gripped at the opposite outer edgesand held clamped in movable tenters. Normally, tenters or tentercarriages on which there are seated pivotable tenter levers hold theedge of the material web clamped in relation to a tenter table.

In the region of the clamping point, the tenter levers must be closedand must be opened once more at the end of the transport device, inparticular of the stretching system.

For this purpose, mechanical opening and closing systems, in which thetenter lever strikes against a rail and is in each case turned over inthe opening or closing direction, are known. Such systems are subject tohigh wear. The primary disadvantage is also the abrupt beginning of theopening or closing movement and the undamped end of the tilting movementof the tenter levers, also designated as knife flaps below, which strikefully against the respectively provided stops.

Magnetic tenter lever actuating are known.

DE-B 1 114 460 discloses a machine for treating fabric webs, of whichthe control elements for pivoting the tenter levers or tenter holdersinclude magnetic rails at the relevant sections of the circulationtrack. The holder levers or tenter levers are in this case configuredsuch that, during their circulation, they pass, at least with anattachment provided on them, as magnet armatures into the region of themagnetic field of the magnetic rails, with the result that the pivotingmovement is forcibly carried out under their action.

According to this prior publication, provision is made for the magneticrail for pivoting the tenter levers to run linearly and parallel to thecirculation path of the tenters. In addition, a further pivoting device,which can be actuated by means of a magnetic coupling, is provided,specifically for pivoting the tenter table cooperating with therespective tenter levers. The further magnetic rail is aligned helicallywith its helix axis parallel to the circulation path, with the resultthat in the relevant region the tenter table, which is held via apivoting lever, is pivoted between two end positions as a function ofthe forward movement of the tenter carriages (that is, of the chaincirculation track).

A magnetic coupling device has also been disclosed by the British GB 9912 45 A1. However, according to this prior publication, provision ismade for the tenter levers, which grip the film web and hold it inrelation to the tenter table, to be pivoted into the open position bymeans of a curved track representing a stop. Only in its final openposition is the tenter lever held by a magnet. For the purpose ofclosing, a lever holding the magnet is pivoted into an open position byrunning onto a wheel, the magnetic coupling being forcibly cancelledthereby and the tenter lever falling down onto the tenter table becauseof its dead weight. The particular disadvantage here is the opening andclosing process, which actually proceeds mechanically, as a result ofwhich the severe mechanical stresses outlined at the beginning lead tothe disadvantages listed there.

A horizontal stretching machine for clamping or tensioning the edges ofa plastic film web by means of a magnetically actuable tenter leverdevice has also been disclosed by EP 0 410 494 B1. In order to open andclose the clamping levers (tenter levers), permanent magnets areprovided here on the tenter lever, opposite the clamping point. For thepurpose of closing or opening the tenter levers in accordance with theopening or closing curve of the tenter levers, stationary magnets arearranged in the inlet and in the outlet region of the stretching machinealong a corresponding rail, the stationary magnets on the appropriateline section, as well as the magnets provided on the tenter levers,being poled to repel. As a result of this repulsion force, the knife ortenter flap is pivoted from its open into its closed position or, viceversa, from its closed into its release position.

This last-named arrangement has in particular the disadvantage that eachindividual tenter lever must be equipped with a separate magnet, whichnot only means a high production cost in relation to the individualknife or tenter flaps but, above all, also contributes to making theoverall system considerably more expensive.

The object of the present invention is therefore, proceeding from thegeneric prior art, to provide an improved, magnetically actuable tenterlever actuating device.

By means of the magnetic tenter lever actuating device according to theinvention, reliable and efficient closing and opening movements of thetenter levers or knives may be carried out. Since the opening andclosing movement is carried out only via the magnetic coupling, themechanical stress is reduced drastically, for example, in relation tomechanical closing and opening devices. Above all, the sound loading isalso considerably reduced.

As a result of the safety device in the form of a mechanical railprovided according to the invention, it is possible to achieve theimportant advantage that, even in extreme situations (in which, forexample, a tenter lever does not open because of extremely high clampingforces), damage to the overall system and/or impairment of the filmbeing produced therewith is/are reliably avoided. This is because, inthe event that the magnetic coupling forces should not be sufficient,further continuous operation of the system without any interruption isnevertheless possible as a result of the safety device according to theinvention. At least by means of the redundant mechanical rail, thetenter lever can be turned over appropriately (this generally hasprimary significance during the opening of the tenter lever, that is,during pivoting over from its closed into its open position, acorresponding mechanical forcible changeover from the open into theclosed position also fundamentally being possible in the case of afurther rail lying opposite).

In this case, in an advantageous refinement of the invention, themechanical rail serving for safety may exhibit resilient behavior atleast in subregions, that is to say it can itself be resiliently formedand/or resiliently supported.

In contrast to DE-B 1 114 460, surprising that, by means of a specificpole shoe shaping and/or by means of a specific configuration of themagnetic return path or armature formed on the tenter lever, providesmagnetic coupling forces which can be considerably increased incomparison with previous solutions. This offers the further advantagethat high magnetic coupling forces can be produced even when magnetswhich are comparatively "weak" with respect to the prior art are used.

Specifically, according to the invention, the improvement is achieved,inter alia, in that the pole shoes are designed in cross-section withincreasing material thickness in the direction of the tenter lever, thatis, in the direction of the coupling attachment, forming the magneticreturn path, of the tenter lever. It has specifically been shown that,as a result, the stray flux may be considerably increased to the benefitof the useful flux, as a result of which the force effect increases.

In an alternative or supplementary embodiment, provision is made for themagnets, preferably comprising permanent magnets, to be arranged betweenthe two pole shoes such that the magnets opposite the tenter leverproject beyond the pole shoes, to be precise preferably by more than 5%,in particular 10% or about 15%, of the height of the pole shoe railswhich accommodate the magnets between them in the manner of a sandwich.

As an alternative and/or supplement thereto, a further increased forceeffect and associated magnetic coupling are achieved by the couplingregion which is formed on the tenter lever and forms the magnetic returnpath or the armature has, in cross-section, a U-shape or at leastapproximately a U-shape. The two U-shaped limbs in this case are locatedin alignment with the two pole shoe rails which are arranged with atransverse offset. By comparison with a return path having a flat orvirtually flat surface in the air gap zone, a considerable increase inthe force and a very much steeper force characteristic curve in relationto the deflection is achieved by this means.

In a particularly preferred embodiment of the invention, all thepreviously explained measures which already individually considerablyimprove the force effect are applied cumulatively.

In a development of the invention, the limb height of the couplingsections of U-shaped cross-section on the tenter lever corresponds toabout 2 to 10 times, in particular 3 to 8 times, above all 4 to 6 times,the height of the air gap zone between U-shaped coupling region and poleshoes. The base region connecting the two limbs of the U-shaped couplingregion preferably has a thickness which corresponds to about 0.5 to 2times, preferably 0.75 to 1.5 times, in particular 1.0 to 1.2 times, thelimb height.

A further improvement may be achieved if the width of the U-shaped limbsof the coupling region are at least slightly narrower than the maximumwidth of the pole shoes adjacent to the coupling region of the tenterlever. In this case the width of the limbs, in relation to the width ofthe pole shoes, can preferably be about 0.6 to 0.9 times, in particular0.8 to 0.9 times, the width of the pole shoes.

In this case it is emphasized that, in spite of the use of anon-contacting magnetic coupling, high safety can be ensured simply byproviding an emergency running rail parallel to the pole shoe rail. If,for any reasons, the tenter lever should not be turned over simply bythe magnetic effect during opening or closing, then the tenter leverwould preferably strike with its end against the emergency running railand, as a function thereof, be turned over into the respectively desiredturned-over position. This could be of importance in practice primarilyonly when the closing forces for fixing the moving material web becometoo great for the magnetic coupling forces. However, after brieflystriking against the emergency running rail and overcoming the clampingforces, the magnetic coupling would as a rule act once more in order topivot over the tenter lever in a deliberate and controlled mannerfollowing the course of the magnetic rail.

Finally, in an alternative or preferred embodiment of the invention,provision is moreover made for the pole shoe rail to be able to escape,in particular to pivot, in the event of a disturbance.

The invention is explained in more detail below by reference toexemplary embodiments. In this case, in detail:

FIG. 1a is a fragmentary schematic plan view of a transport devicerunning on one side of a moving material web and having a magnetic polerail device for pivoting a tenter lever;

FIG. 1b is a schematic illustration of the pivoting movement of the rearend of a tenter lever during the forward movement of a tenter carriage;

FIG. 2 is a schematic cross-sectional view taken along the line A--A inFIG. 1;

FIG. 3 is a cross-sectional view taken along the line B--B in FIG. 1;

FIG. 4 is a schematic enlarged cross-sectional representation through atenter body, shown only in outline, with a tenter lever which can pivotthereon and a magnetic pole rail;

FIG. 5 is an enlarged schematic representation of a detail of themagnetic pole rail in cross-section and of the magnetic return path onthe tenter lever;

FIG. 6 is a diagram to illustrate the characteristic force curve inrelation to the deflection (pivoting) of the tenter lever;

FIG. 7 is a view, essentially corresponding to the FIG. 4, of a portionof a pole shoe rail with an escape device; and

FIG. 8 is a side view transverse to the pole shoe rail with an escapedevice differing from FIG. 7.

Illustrated in FIG. 1a, is a detail of a guide device running on oneside of a moving transport web (for example of a plastic film web in afilm stretching system), along which guide device tenter bodies 1 can bemoved. In the case of a transverse stretching system, this guide devicemay be a tenter chain, in the case of a simultaneous stretching systemthis device may also be, for example, tenter carriages whose distancefrom one another becomes larger in the stretching zone than in the inletzone (stack region). A tenter carriage 1 is partly indicated incross-section only in portions and schematically in FIG. 4 and 5, and isshown there essentially only with reference to the tenter lever and atenter table.

In the top view according to FIG. 1a, for example, a detail of the guidedevice for the tenter bodies 1 which can be moved along this guidedevice is shown, the guide device including an actuating device for themagnetic opening and closing of the tenter levers 3, also designated astenter knives.

In the so-called catching region 7, the tenter levers 3 then stillassume their closed position, in which one edge of a moving material web11 (for example of a film web to be stretched) is held clamped betweenthe clamping region 3' of the tenter lever 3 and the so-called clampingtable 13. In this case, the tenter lever 3 assumes the position which isreproduced with a dashed line in the schematic cross-sectionalrepresentation according to FIG. 4. This position is indicatedschematically in FIG. 2, the longitudinal axis of the lever beingpivotable in FIG. 2 about an axis 17 running parallel to the guide trackor transport direction.

With reference to FIG. 1b, in this case the movement path K_(E) isdepicted in a perspective representation, said path running through theend of the tenter lever 3 during its pivoting movement in the closingdirection when it is being pivoted in accordance with the arrow, along arectilinearly running guide rail, indicated by a dash-dotted line,during the further travel of the tenter carriage. The end of the tenterlever therefore subsequently describes a slightly spiral or helicalpivoting movement about an angle α about its pivot axis 17. L in FIG. 1bdenotes the path length over which the pivoting movement of the tenterlever is executed. In this case, R denotes the length of the tenterlever in relation to its pivot axis 17.

As can be seen from the enlarged schematic cross-sectionalrepresentation according to FIG. 4, a pole shoe rail 21 is arranged, inaxial extension of the tenter lever 3, in the longitudinal direction ofthe guide track/transport device, but running above the latter in asinusoidal or slightly helical manner.

The pole shoe rail 21 in this case comprises two pole shoe rail sections23, running with a lateral offset to each other, between which magnets25 are arranged in the manner of a sandwich, with the pole and magneticflux direction 27 aligned transversely thereto. Use is preferably madeof permanent magnets, but electro-magnetically excitable magnets arealso possible. In this case, a multiplicity of separate magnets 25,situated one behind another, can be provided along the advance rail 21.

From the enlarged schematic cross-sectional representation of FIG. 4 itcan be seen that the pole shoe rail sections 23 broaden conically incross-section in the direction of the tenter lever 3. In the overallexemplary embodiment, this cross-section is of trapezoidal or triangulardesign.

Moreover, the magnets 25 provided between the two pole shoe railsections 23 are arranged such that they are located offset in thedirection of that region of the pole shoe rail sections which tapers incross-section (that is to say away from the tenter lever) and, in thisarrangement, preferably project beyond the height H of the pole shoerail sections by an amount of at least 5%, preferably more than 10%, inparticular by 15%.

The coupling section 29 of the tenter lever 3, which forms the magneticreturn path or armature, runs underneath the so-called pole shoe rail21, whilst forming a narrow air gap D.

In the exemplary embodiment shown, the cross-sectional shape of thiscoupling section 29 is essentially formed in a U-shape.

It can be seen from the enlarged representation of a detail according toFIG. 5 that the height T of the limbs i.e., flanges 31 of the couplingsection of U-shaped cross-section is intended to form about 2 to 10times, preferably 3 to 8 times, in particular 4 to 6 times, the air gapD between the active surfaces 35 of the pole shoe rail 21 and the activesurface 37 of the end sides of the limbs 31 of the U-shaped couplingsection 29.

The thickness R of the base 39 of the coupling section 29, which isU-shaped in cross-section transverse to the transport direction 15, isselected such that this thickness R corresponds to about 0.5 to 2 times,in particular 1.0 to 1.2 times, the limb height T.

A further improvement may be achieved by the limb thickness Bs of thelimbs 31 of the U-shaped coupling section 29 being slightly narrowerthan the maximum thickness of the pole shoe rail sections 23, whichthicken in cross-section in the direction of the tenter lever. It hasproven to be favorable here if this limb thickness Bs corresponds toless than 0.9 times the large pole shoe rail thickness Br. It is morefavorable if the limb thickness Bs in this arrangement corresponds tomore than 0.5 times, in particular more than 0.6, 0.7 or 0.8 times, themaximum pole shoe rail thickness Br.

The mode of action of the magnetically actuable tenter opener/closer isexplained below.

After the tenter lever 1, which is in the dashed position in FIG. 4 andis holding the edge of a material web tensioned with respect to thetenter table, has passed into the catching region 7, the pole shoe rail1 runs slightly sinusoidally in top view, that is to say in a partiallyhelical path.

The magnetic force lines proceeding from the magnet 5 pass over the poleshoe rail sections 23 and the coupling section 29 of U-shapedcross-section. As a result of the magnetic coupling forces effectedthereby, the tenter lever 3 is pivoted about its axis 17 from its closedposition as far as into its maximum open position represented in FIGS. 3and 4, in accordance with the course of the pole shoe rails 21. Byvirtue of the tangential catching region and the tangential releaseregion 43, a continuous and overswing-free pivoting movement results.

In the diagram of FIG. 6, the force variation K in relation to thedeflection A of the tenter lever is represented in relative form. Thecurve K_(n) shows the force variation if the armature-like return path(coupling section 29) on the tenter lever is U-shaped and the pole shoerail sections 23 are shaped with material thickness increasing towardsthe tenter lever. In comparison with this, the force line characteristicmap K₀ is also depicted in FIG. 6, and corresponds to a force variationif use is made of a flat, that is to say not U-shaped in cross-section,return path or coupling section 29 and rail sections 23 which have auniform material cross-section.

During the gripping and clamping of a film web, the closing movement iscarried out by changeover in the opposite direction, using anappropriate pole shoe rail.

Moreover, a safety or emergency running rail, which comprises amechanical stop rail 45, is further shown in the drawings. This stoprail is anchored along the pivoting region, so that it is adjustable ona pole shoe rail carrier 49, by means of screws 47 in such a way that inthe exemplary embodiment shown it projects beyond the lower limit of theactive surface 35 of the pole shoe rail 21 and, in so doing, is arrangedso that it follows the course of the pole shoe rail 21 at the side. Asliding body 51 is provided, at the same height, on the side of thecoupling section 29 of the tenter lever 3. If, for unexpected reasons,in an individual case the magnetic coupling which has been explainedshould not be sufficient, the tenter lever 3, that is to say the slidingbody 51, would strike against the stop rail 45 laterally and, by virtueof the longitudinal course of the stop rail 45, which is sinusoidal orhelical in top view, lever 3 would then be pivoted into the openposition as a result of the effect of mechanical force. Followingmechanical triggering as a result of the sliding body 51 strikingagainst the stop rail 45, the tenter lever, however, would not thenswing over abruptly into the open position but would be caught by themagnetic coupling of the pole shoe 21 and pivoted further in a targetedmanner into its final open position without any overswing.

In this arrangement, the mechanical rail 45 may have a resilientbehavior in subregions, that is to say for example may be resilientlyconstructed and/or composed or at least resiliently supported.

The pole shoe rail sections 23, and also at least the coupling region 29on the tenter lever 3, consist of magnetically highly conductivematerial, in particular of ferromagnetic material.

The pole shoe rail represented in FIG. 4 is reproduced once more usingFIG. 7. Differing from the exemplary embodiment according to FIG. 4,however, the pole shoe rail carrier 49 is now anchored and guided via anescape device 61. In the event of a fault condition, if for example filmresidues should pass into the air gap between the tenter lever end 29and the pole shoe rail 21, the entire pole shoe rail can, for example,escape counter to the gravitational force (and/or the magnetic couplingforces between the tenter levers and the pole shoe rail) by means of thementioned escape device 61; it can escape upward in the exemplaryembodiment shown. The escape device 61 in this case comprises a parallelguide using a plurality of pivotable levers 63 which are arrangedparallel to one another. A position assumed via the escape device isrepresented with a dot-dashed line in FIG. 7.

In an embodiment in accordance with FIG. 8, which is an alternative tothis, it is provided for the escape device 61 to include levers 63'which essentially hang down in the vertical direction and on which a thebottom the pole shoe rail 21 is hung, for example on the pole shoe railcarrier 49. In the case of FIG. 8, several tenter levers 3 are depictedin side view (that is to say in the plane of the material web), saidlevers belonging to different tenter carriages which are normally movedalong the pole shoe rail 21 offset longitudinally from one another. Inthe event of a disturbance (that is to say, if, for example, filmresidues pass into the magnetic gap between pole shoe rail and themagnetic coupling end of the tenter levers 3), the pole shoe rail 21could then--as is likewise depicted with a dashed line--be pivoted fromits lowest position, by means of the levers 63', about its uppersuspensions with a transverse component which is lateral but above allis also directed away from the ends of the tenter levers. After theelimination of the disturbance, a pivoting-back into the functionalposition can be carried out merely by the force of gravity, such as,inter alia, also in the case of the exemplary embodiment according toFIG. 7.

The exemplary embodiments have been described and shown for the case inwhich the magnets 25 used are permanent magnets. Equally well, however,instead of permanent magnets, use may be made of electromagnets or elsea mixture of permanent magnets and electromagnets. If onlyelectromagnets are used or if magnets comprising electromagnets andpermanent magnets are used, these electrically drivable magnets can beoperated either continuously with power or else with pulse excitation.

We claim:
 1. In a transport device for a moving material web having acoupling rail extending at least partially along a circulation path, amagnetic tenter lever actuating device comprising:a tenter body movablealong said path and including a tenter lever mounted for pivotalmovement about an axis on said tenter body between open and closedpositions relative to the web, said tenter lever having a couplingsection; a magnetic coupling between said coupling rail and saidcoupling section for pivoting said tenter lever as said tenter bodymoves along said path defined by said coupling rail; said couplingsection being separated from said coupling rail by an air gap; and anauxiliary safety device for actuating said tenter lever including amechanical system for mechanically pivoting said lever toward said openposition or said closed position in the event of a failure orineffectiveness of said magnetic coupling.
 2. A device according toclaim 1 wherein said safety device comprises a mechanical rail extendinggenerally parallel to said coupling rail and offset relative to saidcoupling rail such that said tenter lever, in the event of failed orinsufficient magnetic coupling, strikes said mechanical rail forpivoting said tenter lever toward one of said open or closed positions.3. A device according to claim 1 wherein said coupling rail comprises apole shoe rail including two pole shoe rail sections laterally offsetrelative to one another, magnets disposed between said rail sections,said coupling section on said tenter lever forming a magnetic returnpath, a thickness of said pole shoe rail sections increasing in thedirection of said tenter lever.
 4. A device according to claim 3 whereinsaid pole shoe rail sections have a cross-section increasing conicallyin the direction of said tenter lever.
 5. A device according to claim 3wherein said pole shoe rail sections have walls generally divergent fromone another in a direction toward said tenter lever.
 6. A deviceaccording to claim 3 wherein said coupling section has a generallyU-shaped cross-section generally transverse to said pivot axis of saidtenter lever.
 7. A device according to claim 6 wherein said U-shapedcoupling section has a pair of flanges and a base, the height of saidflanges above said base and extending toward said air gap being about 2to 10 times the thickness of said air gap between said pole shoe railand said coupling section.
 8. A device according to claim 6 wherein saidU-shaped coupling section has a pair of flanges and a base, said basehaving a thickness about 0.5 to 2 times the height of said flanges abovesaid base.
 9. A device according to claim 6 wherein said U-shapedcoupling section has a pair of flanges and a base, the thickness of saidflanges being at least slightly less than the maximum lateral distanceof said pole shoe rail sections from one another.
 10. A device accordingto claim 9 wherein the thickness of said flanges is about 0.5 to 0.9times the maximum lateral distance of said pole shoe rail sections fromone another.
 11. A device according to claim 3 wherein said magnets aredisposed between said two pole shoe rail sections and project beyond anupper edge of said pole shoe rail sections on a side thereof facing awayfrom said tenter lever.
 12. A device according to claim 11 wherein saidmagnets project beyond a height of said pole shoe rail by at least 5%.13. A device according to claim 1 wherein said mechanical systemincludes a resilient mechanical rail for pivoting said tenter levers inresponse to said tenter levers striking said mechanical rail.
 14. In atransport device for a moving material web having a coupling railextending at least partially along a circulation path, a magnetic tenterlever actuating device comprising:a tenter body movable along said pathand including a tenter lever mounted for pivotal movement about an axison said tenter body, said tenter lever having a coupling section; amagnetic coupling between the coupling rail and said coupling sectionformed on said tenter lever for pivoting said tenter lever as saidtenter body moves along said path defined by said coupling rail; saidcoupling section being separated from said coupling rail by an air gap;said coupling rail including a pole shoe rail; and an escape device formoving said coupling rail away from the coupling region of the tenterlevers.
 15. A device according to claim 14 wherein said escape deviceincludes a plurality of levers for pivoting said escape device away fromsaid tenter levers.
 16. A device according to claim 14 wherein said poleshoe rail is movable away from said tenter levers counter to the forceof gravity.
 17. A device according to claim 14 wherein said escapedevice includes a pair of parallel guides.
 18. A device according toclaim 14 wherein said magnetic coupling includes permanent magnets. 19.A device according to claim 14 wherein said magnetic coupling compriseselectromagnets or electromagnets and permanent magnets.
 20. A deviceaccording to claim 19 wherein said electromagnets are operable withcontinuous power or with pulse excitation.